DES MOINES, Iowa (CNN) -- The 2004 election was about terrorism. The 2006 election was about Iraq.

As the stock market continues to suffer losses, the economy is now the top issue in the presidential race.

What's the big issue going to be for 2008?

Remember "the economy, stupid"? That was in 1992 -- the last time the U.S. had an economic election. Another Bush, another Clinton, and that year the nation experienced an economic downturn.

Now, for the first time in more than four years, a majority of Americans, 57 percent, believe the nation is in a recession, according to a CNN/Opinion Research Corporation poll released Tuesday.

The poll's margin of error on that question was plus or minus 4.5 percentage points.

The economy is now the biggest issue in the presidential campaign. Twenty-nine percent of poll respondents said the economy was their top issue, compared with 23 percent who listed the Iraq war -- a reversal from October's results, when 28 percent listed the war and 22 percent pointed to the economy.

Rounding out the list of top five issues, health care was the top issue for 20 percent of respondents, illegal immigration was the most important issue for 14 percent and terrorism was the key issue for 10 percent.

The poll's margin of error on the top issues was plus or minus 3 percentage points.

Is the economy really that bad? Democrats say yes.

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"I'd describe the economy as kind of a trap door where you're one medical diagnosis or a pink slip or a missed mortgage payment away from dropping through and losing everything," said Sen. Hillary Clinton of New York, the front-runner in the race for the Democratic presidential nomination.

Republicans prefer to look at the big picture.

"What country has had more success in creating a society of fairness and decency, in creating a society in which people move out of poverty, in which people have social mobility, have a chance to succeed?" said former New York Mayor Rudy Giuliani, one of the leading candidates for the Republican presidential nomination.

Undoubtedly true, but what about gas prices, home foreclosures, lagging wages and stock market jitters?

Can Republicans look to national security to save them? Terrorism -- Giuliani's issue -- ranks fifth in importance out of five issues right now.

The security situation in Iraq may be improving, although that, too, is in dispute.

"The senator from New York, Sen. Clinton, said, quote, 'I would have to suspend disbelief in order to believe that the surge is working,' " said Sen. John McCain of Arizona, another Republican presidential hopeful. "Well, anyone today would have to suspend disbelief to not believe that the surge is working."

But there's no evidence of any increase in public support for the war in Iraq. According to the poll, 69 percent, the highest number yet, want to withdraw some or all U.S. troops.

There's been some good news about Iran. A National Intelligence Estimate finds that Iran may have halted its nuclear weapons program for the time being.

But that news may not do Republicans much good. Nearly half of Americans, 54 percent, believe the Bush administration deliberately misled them about whether Iran was attempting to develop nuclear weapons. The poll's margin of error on that question was plus-or-minus 4.5 percent.

President Bush's job approval is 32 percent. No wonder Republicans as well as Democrats are trying to run as agents of change.E-mail to a friend